A. c.-d. c. testing device



April 23, 1957 4R'. A. slc-:l-lo

A c .-D c. TESTING DEVICE Filed Aug. 31. 1953 INVENToR ,Qd/WAN A. s/c//o ATTORNEY United States Patent 'C3 i A. C.D. C. TESTING DEVICE Roman A. Sicho, Elmhurst, N. Y., assignor to Electronic Instrument Co., Inc.

Application August 31, 1953, Serial No. 377,355

8 (Cl. S24-72.5)

My present invention relates to improvements in testing devices or probes for electric circuits requiring the use of more than one type of source of electric energy, such as sources of alternating and of direct current.

Particularly where the testing device is designed to cooperate with a highly sensitive measuring instrument, such as a vacuum tube voltmeter or the like, it is preferable to have the resistor in the probe rather than in the instrument in order to reduce contact potential and to reduce pickup; it is also necessary to adapt the impedance of a probe to that of the circuit to be tested, in order not to overload the meter. The impedance of the circuit to be tested, however, will in many instances be different for alternating and for direct current, being usually larger in the former case. It has, therefore, been the practice to provide two separate probes for testing with A. C. and D. C. current sources, respectively, the D. C. probe incorporating an additional resistance to compensate for the aforementioned difference in circuit impedance. The use of two probes entails, of course, considerable inconvenience, delay and expense.

It is, accordingly, an object of my present invention to provide a testing device of the aforementioned character having means for quickly and easily converting it from a probe suitable for one type of electric energy (e. g. direct current) into a probe adapted to be used with another type of electric energy (e. g. alternating current) and vice versa.

It is another object of this invention to provide a convertible probe as set forth in which reversible switch means adapted to effect the conversion are coupled with means for positively indicating to the user the condition in which the device has been placed, thereby obviating the risk of using the probe in combination with a source of current to which it has not been adjusted.

A further object of the invention is t-o provide reversible switch means, for the purpose indicated above, so positioned as to occupy a minimum of space and to be readily accessible for operation Without unduly increasing the bulk of the probe.

The foregoing objects are realized, -in accordance with a feature of my invention, by the provision of a rotary switch member which concentrica-lly surrounds the xed contact electrode of the probe and carries markings selectively displayed through a window in the tubular probe housing, these markings indicating whether the switch member, by its operation, has conditioned the probe for, say, A. C. or D. C. testing.

The above and other objects and features of this invention will become more fully apparent from the following description of a now preferred embodiment, reference being had to the accompanying drawing in which:

Fig. l is a perspective view of a testing device according to the invention;

Fig. 2 is an axial section through the tubular housing of the probe proper;

Fig. 3 is a perspective view of the switch member and associated parts removed from the housing;

.Patented Apr. 23, 195'12' ice 2 Fig. 4 is a section taken on the line IV-IV of Fig. 2, illustrating the AC position of my device; l

Fig. 5 is a section Isimilar to Fig. 4 but illustrating the DC position of my device; and

6 is a circuit diagram of the testing device shown in The testing device shown in the drawing, whose eilements have been uniformly designated throughout the sev-v eral views,` comprises a contact electrode or probe tip 1 projecting from one end of a tubular housing 3.l A'lead wire 5, projecting from the opposite end of the housing 3,

is connected to another tip' 17 adapted to engage a terminal of a voltmeter, current source etc. (not shown).

Insulated lead wire 5 is secured to the housing 3 by means of an insulating plug 4 which is immobilized with respect to the housing by a pin 12. At 15 there is shown within the housing a junction between an extremity of wire S, an end of a contact spring 7 and a terminal of a resistor 10 whose other terminal is joined at 16 to contact electrode 1. A mounting board 6, internally supported by the wall of housing 3, serves as an insulating base for the elements 1, 5, 7 and 10.

Rotatably held within the housing 3 opposite plug 4, by means of retaining ring 11, is a knurled'or milled head 2 serving as a control member for the switch represented `by contact spring 7 and electrode 1. Head 2, concentrically surrounds the electrode 1 and on its inner enid bears two insulating projections 13, 14 lying in lone plane with this electrode. diametrically opposite positions in which the projections 13, 14 are substantially ush with electrode 1 and allow and, as best seen inFig. 5, head 2 also has twlo diametrically opposite positions in quadrature with the iaforernenl tioned ones in which contact spring- 7 is held out of eng gagement with electrode 1 by either one of the two projections 13, 14. A reduced portion of head 2 bears a scale 9 comprising the markings AC and DC, Fig. 3, visible through a window 8 in housing 3 when the head is in the position of Figs. 4 and 5, respectively.

It will thus be apparent that in th'e AC position of head 2 (Figs. 2 and 4) the switch 1, 7 effectively shunts the resistor 10, thereby reducing the internal resistance of the device and adapting it for use in series with an A. C. source; conversely, in the DC position of head 2 (Fig. 5 the switch is open, as also illustrated in the diagram of Fig. 6, whereby resistor 10 is effectively in circuit and thedevice can be used in series with a D. C. source. It will be apparent, however, that according to the broader aspects of the invention it is possible to replace the resistor 10 by some other impedance if use of the device for purposes other than those specifically outlined is desired; the invention, accordingly, is not limited to the particular arrangement described and illustrated by may be embodied in various modifications and adaptations without departing from the spirit and scope of the -appended claims.

I claim:

1. An electric testing device comprising an elongated `contact electrode, a tubular housing surrounding said electrode, a control member rotatably held in said housing and concentrically surrounding said electrode, impedance means within said housing, conductor means extending from said housing, switch means in said housing for selectively connecting said impedance means in circuit with said electrode and said conductor means and for effectively removing said impedance means from `said circuit, and means including said control member for operating said switch means.

2. A device according to claim 1, wherein said switch means comprises a contact element adapted to engage As bestseen in Fig. 4, head 2 has two said electrode, said control member being provided with actuatingv means for removing said contact'element' from said elect-rode in a selected position `of 4said control member.

member; isi provided withV .indicator131ca11.8 said'` .housing being provided with a formationcooperating withF said,

.indicatorAv means ,to indicate the instantaneous position .of said switch means.

VL Anelectric.-testinadevice cqmprising a tubular heus and said conductor, and at least one projection on said headv positioned alongside said extending portion and adapted tobreak Contact between said electrode andsaid spring inone position of said head while ali'owing. such Contact in another position of said head.

5. A device according to 'claim'4, wherein said head is provided with a rst marking visiblethrough a cutout inrthe housing in said one position and withasecond marking visible through said cutout yin said other position of said head.

6. An electric testing device. comprisingran elongated contact electrode, a tubular ,housing surrounding said electrode, a control member rotatablyh'eld in said housing and eoncentrically surrounding said electrode, impedance means within said hou-sing, conductor means extending from said housing, switch meansin said housing for selectively connecting said impedance means in circuit with said electrode and said conductor means and for effectively removing-.said impedance'means from said circuit, said switch means comprisingxa spring conductively connected to said,

conductor means and .resiliently urged toward said elec- 3. A device accordingtoclaim Lvvherein said control trode, and said control member being provided with actuating means? for removing said springfrom said electrode in a seiected position of said control member.

7. An electric testing device comprising an elongated contact electrode, a tubular housing surrounding said electrode, a control member rotatably held in said housing and concentrically surrounding said electrode, impedance means within said housing, conductor means extending from said housing, switch means nsaidrhousing for selec tively connecting said impedance means in circuit with said electrode and said conductor` means Vand for eiectively removing said impedance means from said circuit, said yswitch-means ,comprising a contact` element. adapted to engage said electrode, and said control member being provided with a pair of projections straddling said electrode and interposing themselves between said electrode and said contact element in respective selected positions of Asaidcontrol member yet 4lying parallel to the surface of saidcontact elementin other positions of said control member.

8. Anv electric testing device comprising an elongated contact electrode, a tubular housing surrounding said elecltrodeia control member rotatably heldin said housing and concentrically surrounding said electrode, said control member being provided with a plurality of indicator markingsselectivelyviewable throughv al cutout in said housing, impedanerneans within said housing, conductor meansex- :tendina.frQm-aidhousins, switch means in said hQuSins forselectively..ennnectngsad impedance means .in circuit with saidelectrode and ,conductor means and for; eiectiyely removingsaidcimpedance, means from, said circuit, and means including said control member for operating .said switchmeans.

:References Citedin thele .of this patent UNITED 'STATES PATENTS Y 1,560,278` Mahan Nev. 3, 1,925 1,17 07,05 l COIOSO .Man 26, 1929 21,488,328

tRider v Nov. 15, 1949 

